Process for polymerizing aldehydes



Dec, 16, 1958 n. H. BAER ETAL 2,864,827

l PROCESS FOR POLYMERIZING ALDEHYDES Filed Nov. l5, 1954 AORNS ias!! 2,864,327 PRCESS FR ULYMERIZWG ALDEHYDES e Donald El. haar, `Los Angeles, Calif., and .lohn E. Mahan,

Bartlesville, Gilda., assignors to Phillips Petroleum` Company, a corporation of Delaware e Application November l5, 1954, Serial No. 468,874

7 anims. (ci. asa- 340) This invention relates to a process for polymerizing aldehydes. f

Heretofore, aldehydes have been catalytically converted to polymeric materials, usually trimers, with an acid catalyst. When a material, such as sulfuric acid, is used as catalyst, a rapid conversion of the aldehyde takes place but a large amount of tarry material is formed` which tends to pollute the polymeric product, plug the process lines, and cause other operating diiliculties. Where a weaker acid, such asy phosphoric acid, is used as catalyst, less tarry material 4is produced but the reaction rate is too slow for satisfactory operation on a kcommercial scale.

We have discovered that therpolymerization of aldehydes can be carried on at a rapid rate without the for; mation of excessive tarry by-products by utilizing a mixed catalyst composed of sulfuric acid and phosphoric acid. the rapid reaction rates possible with sulfuric acid are retained and, yet, the formationwof undesirable by-products-.

' is greatly minimized.

Accordingly, it is` an object of our invention toprovide v an improved catalyst for the polymerization of aldehydes.,

It is a further object toprovide a catalyst which .will eifect polymerization of aldehydesat a rapid rate without the formation of excessive amounts of tarry products.

Various other objects, advantages and lfeatures of the invention will become apparent from the following detailed description taken in conjunction withthe accompanying drawings, in which:

The figure is a flow diagram illustrating the process of this invention.

Referring now to the drawing in detail, acetaldehyde` or other aldehyde tobe converted is stored in a tank 10. While the catalyst of this invention is particularly suitable for the commercial production of paraldehyde from` acetaldehyde and is described as such, it is broadly applicable to polymerizable aldehydes, specifically aliphatic.

aldehydeshaving two to seven carbon atoms, such as propionaldehyde, or n-heptaldehyde.`

The mixed acid catalyst is maintained ina storage tank il, and is composed of sulfuric acid and phosphoric acid. The improved results attributable to the catalyst of this invention are most apparent where the ratio byV weight of sulfuric acid to phosphoric acid varies from 2 1 to l r 2 based on 98% sulfuric yacid and 85% phosphoric acid. This results in a color index at thepoint of acid injection, as measured on the Gardner Varnish Scale, of -13 or less, due to the formation of tarry products, as compared to a color index of l to 18 where sulfuric acid is employed as the sole catalyst. In commercial operation, this ratio is maintained between the values e of l l to 1 2, resulting in a color index, as measured on the Gardner Varnish Scale, or 3 or less.

The aldehyde andcatalyst are charged through lines l2 and lila, respectively, insuch proportionsas to maintain the weight percent ofsulfuric acid in the catalyst, based economy, rapidity of conversion, and color specification,

Surprisingly when operating with this catalyst,`

the temperature is maintained within the range of 100 to In commercial operations with a sulfuric acid catalyst, substantial diiiculties were encountered due toplugging of the line i211, which was alt inch pipe, at its connection to conduit i3, which was a S-inchpipe. At .this

junction, there was, `in elfect, a contact zone between bodies of sulfuric acid and aldehyde material.,`

In accordance with the invention, theseplugging difculties are eliminated or substantially minimized by utilizing a mixed'sulfu'ric acid-phosphoric acid catalyst in a weight ratio of l l to l 2, and a substantial improvement of the plugging condition is obtained where said Weight ratio is within the range of 2 l to 1 l.

It is a feature of the invention that such elimination of plugging difficulties occurs Without impairing the rapid reaction rate resultingv from the sulfuric acid in the catalyst; in fact, the addition of the phosphoric acid may even increase the polymerizationy rate due to the additionalcatalytic action of the phosphoric acid.

In particular, conversion of a substantially pure mixture of 72% paraldehydeand 28% acetaldehyde to the equilibrium mixture of acetaldehyde andparaldehyde can be readily obtained with `a residence time in the circulating7V stream of as little' as 25 minutes with the mixed sul-r furic-phosphoric catalyst of this invention, the same time as required for the system to reach equilibrium with the sulfuric acid catalyst. WithV phosphoric acid as the sole catalyst, the conversion of paraldehyde to the equilibrium mixture is only 20% complete after a residence time of minutes and, with a hydrochloric acid catalyst, the conversionto the equilibriumxmixture was 50% complete after a residence time of 60 minutes. Results with a trichloroacetic acidcatalyst and a hydrobromic acid catalyst were muchl poorer, as regards conversion, than those obtained with the phosphoric acid catalyst.

In commercial operation, impurities such as water, and ethylene oxide, which may be present in small quantities, retard the rapidity withwhich the equilibrium and quantity of impurities present in the circulating stream.

In the circulating stream, a mixture of essentially 72 partsof paraldehyde and 38 parts of acetaldehyde is converted to the equilibrium mixture, for example, 82 parts of paraldehyde and 18 parts of acetaldehyde.

For best results, the pressure should vary within the range of 5 to 60 `pounds perA square inch gauge. In commercial operation, the pressure is close to 45 pounds per square inch gauge. The pressure should be su'icient to maintain reactants in liquid phase.

The polymerized material leaves the reactor l5 through a conduit i6 wherein it is immediately contacted with an excess, such as of a neutralizing agent which is introduced into the conduit l5 from a tank 17.7-,

Suitable neutralizing agents for this purpose are the Patented Deo. 16,. lh,

i 3 basic salts or hydroxides of the alkali or alkaline earth metals, such as sodium carbonate, calcium hydroxide, potassium carbonate, potassium hydroxide, and barium hydroxide. An excess of neutralizing agent is used in each case, compared with the quantity required to neutralize the acid present in the reactor effluent.

In the manufacture of Z-methyl-S-ethylpyridine with paraldehyde as a starting material, 2-methyl-5-ethylpyridine can be advantageously utilized as the neutralizing agent, since this is the material formed from the paraldehyde in a subsequent reaction thereof with ammonia.

Another advantageous neutralizing agent is a mixture of sodium acetate and ammonium acetate. Where this material is used, no supplemental addition of Z-methyl- 5-ethylpyridine is required to prevent reversion of paraldehyde, as is thecase where sodium carbonate is used as the neutralizing agent, and plugging difliculties in or downstream of the neutralizer are eliminated or greatly minimized. Further, salt precipitation in the neutralizer and paraldehyde loss in the aqueous discharge are eliminated or greatlyminimizedi t The neutralized material passes from conduit 16 to a separator tank 18, the neutralized product leaving the tank through a conduit 19 while heavy materials separated in the tank 13 are withdrawn downwardly through a conduit 20 and fed to a sludge tank 21. Suitable conditions for commercial operation of the separator vessel are a pressure of 40 pounds per square inch gauge and a temperature of 110 F.

The neutralized material withdrawn from conduit 19 is fed to a vaporizer 22 which is heated by a steam coil 23. In the production of paraldehyde, suitable conditions for the vaporizer 22 are a pressure of 32 pounds per square inch gauge and a temperature of 338 F. From the vaporizer, heavy material is discharged through a con-V duit 24 to the sludge tank 21 while the vaporized material passes through a conduit 25 to a fractionation column 26.

In this column, the polymerized aldehyde is separated from the non-polymerized material, the bottoms product being withdrawn through a line 27 and a cooler 28 to a product storage .tank 29. The overhead product from column 26 is withdrawn through a line 31 and passed through a condenser 32 to anA overhead accumulator 33. A portion of this top product is fed as reflux to the top of the column through a line 34 While the remainder of the overhead product is passed through a line 35 to the circulating stream, advantageously at a point Where the cooler material is introduced into the reaction vessel, as shown. tionator 26 are a top temperature of 126 F. and a bottom temperature of 323 F. t

From the foregoing, it will be evident that we have achieved the objects of our invention in providing a complete system for the polymerization of an aliphatic aldehyde, such as acetaldehyde, with a mixed `sulfuric acidphosphoric acid catalyst which produces a high conver-` Suitable conditions for operation of the fracwe have disclosed conditions particularly suitable for the f commercial production of paraldehyde with this catalyst.

While the invention has been described in connection with present, preferred embodiments thereof, it is to be understood that this description is illustrative only and is not intended to limit the invention.

We claim:

1. The method of polymerizing an alkyl aldehyde hav ing two to Seven carbon atoms which comprises contacting said aldehyde with an acid catalyst composed of sulfuric acid and phosphoric acid,` said acids being in the weight ratio of 2 1 to` 1 2. l

2. A method of polymerizing an alkyl aldehyde having two to seven carbon atoms whichcomprises contact l ing said aldehyde with a catalyst composed of sulfuric acid and phosphoric acid in the weight ratio of 2 z 1 to 1 :2, said sulfuric acid being present in an amount of 0.05 to 1.0 percent by weight based on said aldehyde, and maintaining the catalyst in contact with the aldehyde for a period of from 25 to 240 minutes at a temperature of 32 to 120 F. and at a pressure sufficient to maintain a liquid phase.

3. The method of polymerizing an alkyl aldehyde having two to seven carbon atoms which comprises contacting said aldehyde with a catalyst composed of sulfuric and phosphoric acids in the weight ratio of l 1 to 1 2, and maintaining the catalyst in contact with the aldehyde for a period of 25 to 240 minutes at a temperature of to 120 F. and at a pressure sufficient to maintain a liquid phase.

4. The method of polymerizing acetaldehyde to form paraldehyde which comprises contacting acetaldehyde with a catalyst composed of sulfuric and phosphoric acids in the weight ratio of l 1 to 1 2, said sulfuric acid being present in the amount of 0.05 to 0.2% by weight, based on the feed, maintaining the catalyst in contact with said acetaldehyde for a period suicient to provide an equilibrium mixture at a temperature of 100 to 120 F. and at a pressure sufiicientto maintain a liquid phase.

5. The method of polymerizing an alkyl aldehyde having two to seven carbon atoms which comprises circulating a stream of said aldehyde in a path which includes a reactor and a cooler, continuously adding a sufiicient amount of a mixed acid catalyst to said stream to maintain a concentration of sufuric acid of 0.05 to 1.0 percent by weight based on the aldehyde, said catalyst being composed of sulfuric acid and phosphoric acid in the weight ratio of 2 1 to l 2, continuously withdrawing a portion of said stream, contacting the withdrawn material with an excess of an alkaline neutralizing agent, fractionating the neutralized material to separate it into a polymer-containing portion and a portion composed of unreacted aldehyde, recycling the unreacted aldehyde to the circulating stream, and recovering the polymer-containing portion as a product.

6. The method of polymerizing acetaldehyde which comprises circulating a stream of said acetaldehyde in a path which includes a reactor and a cooler, continuously adding a mixed acid catalyst to said stream, said catalyst being composed of sulfuric acid and phosphoric acid in the ratio of 1 l to `l 2, continuously adding acetaldehyde to said stream upstream of the region of catalyst addition, maintaining an acetaldehyde residence time in said stream of 25 to 240 minutes, said sulfuric acid being present in the amount of 0.05 to 0.2% by weight, based on the feed, continuously withdrawing a portion of said stream, contacting the withdrawn material with an excess of an alkaline neutralizing agent, fractionating the neutralized material to separate it into a paraldehyde fraction and an acetaldehyde fraction, recycling the acetaldehyde fraction to the circulating stream, and recovering the paraldehyde fraction as a product.

7. The method of polymerizing acetaldehyde to paraldehyde which comprises contacting acetaldehyde with a catalyst consisting essentially of a mixture of sulfuric acid and phosphoric acid, said acids being in the weight ratio of 2:1to 1:2.

References Cited in the file of this patent UNITED STATES PATENTS 1,300,451 Morton et al. Apr. 15, 1919 2,318,341 Thompson May 4, 1943 2,369,504 Walker Feb. 13, 1945 2,442,942 Tuerck et al. June 8, 1948 2,571,759 Quinn et al. Oct. 16, 1951 FOREIGN PATENTS 557,447 Germany Aug. 23, 1932 342,668 Great Britain Feb. 3, 1931 

1. THE METHOD OF POLYMERIZING AN ALKYL ALDEHYDE HAVING TWO TO SEVEN CARBON ATOMS WHICH COMPRISES CONTACTING SAID ALDEHYDE WITH AN ACID CATALYST COMPOSED OF SULFURIC ACID AND PHOSPHORIC ACIDS, BEING IN THE WEIGHT RATIO OF 2:1 TO 1:2. 